The present invention generally relates to inkjet and other types of printers and more particularly, to a system and method for using lower data rates for high nozzles per inch [NPI] printheads.
An inkjet printer produces a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes xe2x80x9cdot locationsxe2x80x9d, xe2x80x9cdot positionsxe2x80x9d, or pixelsxe2x80x9d. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more print cartridges each having a printhead with a nozzle member having ink ejecting nozzles. The carriage traverses over the surface of the print medium. An ink supply, such as an ink reservoir, supplies ink to the nozzles. The nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
In general, the small drops of ink are ejected from the nozzles through orifices by rapidly heating a small volume of ink located in vaporization chambers with small electric heaters, such as small thin film resistors. The small thin film resistors are usually located adjacent the vaporization chambers. Heating the ink causes the ink to vaporize and be ejected from the orifices. Specifically, for one dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor of a selected vaporization chamber. The resistor is then heated for superheating a thin layer of ink located within the selected vaporization chamber, causing explosive vaporization, and, consequently, a droplet of ink is ejected from the nozzle and onto a print media. One very important factor in assuring high print quality is the placement of the ejected droplet upon the print media.
One problem that exists is assuring the accurate placement of ink droplets on the print media is the reduction or compensation for noise. Noise may be produced from mechanical or electrical or other sources and results in the random clustering of ink droplets on the print media forming bands. This may be offset by introducing intentional noise, dithering patterns, or asymmetric resolutions of the rectangular grid locations to be printed. Systems using large numbers of nozzles and/or multiple passes may offset banding through passive redundancy or active nozzle replacement. These systems would require higher data rates, increased buffer memory, and higher firing pulse rates.
Another problem in producing high print quality is controlling the number of passes and the number of nozzles required to produce the image. In a single pass a print-head may utilize 2400 nozzles per inch (npi) in printing 1200 dpi to the print media. Another print-head configuration may use 600 npi in a single pass with two 4 ng drops per nozzle, in printing 600 dpi to the print media. The former would require increased data to the print-head, increased printed data and therefore an increase in fire pulses to the heater elements of the print-head. Therefore, what is needed is a more efficient system of producing high quality printouts.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a system and method for using lower data rates for high nozzles per inch printheads.
The printing system of the present invention includes a printhead assembly and an ink supply for printing ink on print media. The printhead assembly includes a printhead body, ink channels, a substrate, such as a semiconductor wafer, a nozzle member and a barrier layer located between the wafer and nozzle member. The nozzle member has plural nozzles coupled to respective ink channels and is secured at a predefined location to the printhead body with a suitable adhesive layer. The printhead has a controller which can be firmware, software or any suitable processor that can control the ejection of ink from the plural nozzles. The controller can be defined in the integrated circuit as receiving data stored in the data in the buffer memory, assigning primitive addresses in the heater array from the data, and determining the firing pulse rate of the heater elements in the heater array. The controller can be created by any suitable integrated circuit manufacturing or programming process.
The controller determines the firing order of the nozzles in a single or multiple swath. The location of a dot produced by a nozzle can also be changed in a column by changing the sequence in which the addresses of primitives are fired. A printhead may have up to 12 addresses per primitive. In an embodiment of the current invention every odd numbered nozzle is offset to the even numbered nozzles so that the horizontal data is encoded in a vertical axis. This feature maintains the resolution of the print swath in the horizontal axis and decreases the data rate required to produce the print by a factor of 2.